Anderson has been active in supporting numerous charities and humanitarian organizations. She is an honorary spokesperson for the Neurofibromatosis (NF) Network and a co-founder of South African Youth Education for Sustainability (SAYes).

Following the move to Grand Rapids, Anderson went through a rebellious stage; experimenting with drugs, dating a much older boyfriend and having a punk appearance (dyeing her hair various colours, shaving the sides of her head, sporting a nose piercing and an all-black wardrobe).[10][12][14] She was put in therapy at the age of 14.[13] Anderson listened to bands such as Dead Kennedys and Skinny Puppy. She was voted by her classmates: "class clown", "most bizarre girl" and "most likely to be arrested". She was, in fact, arrested on graduation night for breaking and entering into her high school in an attempt to glue the locks of the doors.[15] She later managed to reduce the charges to trespassing.[16]

Anderson is bidialectal. With her English accent and background, she was mocked and felt out of place in the American Midwest and soon adopted a Midwestern accent. To this day, her accent depends on her location, as she easily shifts between her American and English accents.[23] In May 2013, during an interview with BlogTalkRadio, Anderson addressed the matter of her national identity: "I've been asked whether I feel more like a Brit than an American and I don't know what the answer to that question is. I know that I feel that London is home and I'm very happy with that as my home. I love London as a city and I feel very comfortable there. In terms of identity, I'm still a bit baffled."[24]

"We got a lot of letters all the time, and I was told quite frequently by girls who were going into the medical world or the science world or the FBI world or other worlds that I reigned, that they were pursuing those pursuits because of the character of Scully. And I said, 'Yay!'"

In 1996, Anderson narrated the television documentariesSpies Above[36] and Why Planes Go Down.[37] While hosting the BBCdocumentary series Future Fantastic, she became impressed by the featuring theme music of the show, by the electronic duo Hal and initiated a collaboration with them. In 1997, Anderson provided spoken word vocals and starred in the music video for their single “Extremis”, which was frequently aired on MTV. She also helped to assemble an album of electronic music, Future: A Journey Through The Electronic Underground, for Virgin Records, which won praises from European music critics.[38][39]

In October 2014, Anderson published her first book, A Vision of Fire, co-authored by Jeff Rovin. The book is the first novel of The EarthEnd Saga trilogy and is described as "a science fiction thriller of epic proportions".[74][75] In February 2015, Anderson narrated the medical documentary The Widowmaker.[76] In December 2015, Anderson and Rovin published their second novel of the The EarthEnd Saga series, A Dream of Ice.[77] In January 2016, Anderson portrayed Anna Pavlovna Scherer in BBC One's television adaptation War & Peace.[78] The same month, she was back portraying FBI Special Agent Dana Scully in a six-episode miniseriesrevival of The X-Files.[79] Anderson has fought and succeeded in securing equal pay with her male co-star on The X-Files in the ’90s and again in 2015, when negotiating her salary with the network. She has been outspoken about the ongoing issue throughout the years.[80]

From April 23, 2016 through June 4, 2016, Anderson reprised her role of Blanche DuBois in A Streetcar Named Desire on stage at the new St. Ann's Warehouse in Brooklyn, NYC.[81] On September 13, 2016, Anderson and Rovin published The Sound of Seas; their third and final novel of The EarthEnd Saga trilogy.[82] The same month, she was back portraying DSI Stella Gibson in the third series of The Fall.[83]

On March 7, 2017, Anderson and the journalist-activist Jennifer Nadel will publish their self-help guide book for women, titled WE: A Manifesto for Women Everywhere.[88] The book is described as an "urgent and timely book for women, which offers a dramatically new path to fulfillment".[89] Anderson stated that the book is a "call-out to all women around the world – and by women I include girls, transgender, anyone who identifies themselves as being intrinsically female."[90] In June 2016, it was announced that she will portray Media in American Gods – a TV series adaptation of Neil Gaiman's novel of the same name.[91] In September 2016, it was announced that Anderson has joined the cast of the upcoming drama Andorra, alongside Joanna Lumley, Guy Pearce and Toni Collette.[92]

Anderson married her first husband, Clyde Klotz, an X-Files assistant art director, on New Year's Day 1994, in Hawaii in a Buddhist ceremony. Their daughter, Piper Maru, was born on September 25, 1994.[6][12] Showrunner Chris Carter, Piper's godfather, named the X-Filesepisode of the same name after her. Anderson and Klotz divorced in 1997.[12] On December 29, 2004, Anderson married Julian Ozanne, a documentary filmmaker, on Lamu Island, off the coast of Kenya. Anderson announced their separation on April 21, 2006.[98] Anderson and former boyfriend, businessman Mark Griffiths, have two sons: Oscar, born on November 1, 2006[99] and Felix, born on October 15, 2008.[100] She ended their relationship in 2012.[101] In March 2012, Anderson told Out magazine about her past relationships with women.[14] Anderson identifies as heterosexual[102][103] and in an interview with the Evening Standard in December 2014, she stated: "I am an actively heterosexual woman who celebrates however people want to express their sexuality."[7] In an interview with the Telegraph in March 2015, Anderson said that she was not closed to the idea of entering another same-sex relationship, adding: "To me a relationship is about loving another human being; their gender is irrelevant."[104]

Anderson self-identifies as a feminist.[105][106] In an August 2014 interview with Glamour magazine, Anderson said: "I have feminist bones and when I hear things or see people react to women in certain ways I have very little tolerance."[107] Anderson has several tattoos; all of them, as she described, are in some way about "peace of mind, right mind, right action".[15] She practices meditation daily.[108]

Anderson resides in London with her three children, where she has lived since 2002.[43]

Anderson has been active in supporting numerous charity organizations, global and social causes, as well as running her own humanitarian ventures. Anderson is known to support the LGBT community, particularly youth. She supports The Trevor Project organization, focused on suicide prevention efforts among LGBTQ youth and attended three of the Trevor Project's "Cracked X-Mas" events to benefit the organization.[109][110] In 2013, Anderson was made a patron of the Charles Dickens Statue Fund, and was instrumental in securing the funding for UK's first Dickens statue, located in Portsmouth, Hampshire.[111] In June, 2016 Anderson become a patron of the Temple Legal Centre, a London-based organization that assists people through the legal process by providing them free family law advice and support.[112] In June 2016, Anderson expressed her support for the United Kingdom to remain a member of the European Union in the run-up to June's referendum on that issue.[113][114]

Anderson is an honorary spokesperson for the Neurofibromatosis (NF) Network. She often holds auctions with the profits benefiting the NF Network.[115] Her brother Aaron died from the disease in 2011.[22][19] In May 1996, Anderson addressed the United States Congress urging for more education and funding for NF research projects.[116] She partners with Doodle 4 NF – an annual fundraiser for the NF Network.[117] She also supported the Children with Tumours organization[118] and the Global Genes movement, which is devoted to helping children with NF.[119]

In 2008, Anderson co-founded South African Youth Education for Sustainability (SAYes), which aids in empowering marginalised young people in South Africa through youth mentoring. The trust provides youth leaving children's homes with guidance that enables them to develop their skills, further their education, and source suitable housing in order to participate in society as independent adults.[120]

While filming The Last King of Scotland in 2005, Anderson started a crowdfunding venture that benefited the Alinyiikira Junior School in Kampala, Uganda. She ran the philanthropic project until 2011.[121] Anderson is a member of the board of directors for Artists for a New South Africa[122][123] and a campaigner for ACTSA: Action for Southern Africa.[124][125] She was a patron of the Friends of Treatment Action Campaign (FoTAC) which worked with the Treatment Action Campaign in South Africa to ensure greater access to treatment to reduce the effects of HIV and prevent new infections.[126] Anderson also supported Buskaid – a charitable trust aiming to help young black musicians in South Africa.[127][128]

Anderson is a supporter of various women's organizations and social movements. She has been a long-time supporter of the Feminist Majority Foundation (FMF). In 1996, Anderson became FMF's spokesperson and participated as a team leader in the FMF's Million4Roe campaign. In March 1999, she attended an FMF event to stop gender apartheid in Afghanistan and in April 2002, she appeared on Hollywood Squares to benefit the FMF's campaign to aid Afghan women and girls.[129] Anderson participated in Eve Ensler's Vagina Monologues, including a stage performance on February 14, 1999.[41] Anderson is a supporter of Ensler's V-Day movement aiming to end violence against women and girls.[130]

In late 2010, Anderson and other artists joined a campaign to boycott Botswana diamonds over the government's treatment of the Kalahari San.[143] Anderson supports tribal rights charity Survival International, an organization that champions tribal peoples around the world and in early 2010 she participated in a performance in a London stage fundraiser for its cause.[144] In February 2011, Anderson narrated a short film about recent footage of an uncontacted tribe, in which the Amazon Indians were spotted from the air on the Brazil-Peru border. Anderson has said: "What comes across powerfully from this amazing footage is how healthy and confident these people appear. I hope they can be left alone – but that will only happen if the loggers are stopped."[145] In June 2011, Anderson became an ambassador for Survival International.[146] In September 2015, Anderson was among the artists who signed a letter calling for a new approach to conservation that would respect tribal peoples' rights.[147]

Anderson is an active member of People for the Ethical Treatment of Animals (PETA) and supports animal rights.[148] In 2006, Anderson was honoured with PETA's Humanitarian Award for her consistent work for the organization.[149] In October 2008, Anderson narrated for PETA a video of undercover footage from rabbit fur farms in China and France.[150][151] In April 2009, Anderson sent a letter – on behalf of PETA – to every Member of the European Parliament (MEP) urging to vote in favor of the proposed directive on the protection of animals used in scientific procedures.[152] In October 2010, Anderson participated in 10:10’s controversial short film, No Pressure, as part of the global warming mitigation campaign’s aim to encourage the reduction of CO2 emissions.

In 2012, she joined Greenpeace in standing with the people of Brazil for a zero deforestation law to save the Amazon.[153] In 2013, Anderson backed the Cheetah Conservation Fund by creating a short film together with the fund, advocating CCF's action to prevent the extinction of the cheetah.[154] In 2013, Anderson joined the Fishlove campaign, supporting the fight against unsustainable fishing practices that harm the marine ecosystem.[155] In October 2015, Anderson wrote a letter to the Indian Ministry of Health and Family Welfare requesting a ban on repeat experiments on animals in toxicity tests.[156] In November 2015, Anderson was named a friend and supporter of Positive Luxury, a company that informs consumers on brands' commitment to quality, craftsmanship, service and sustainability.[157][158]

In 1996, Anderson was voted the "Sexiest Woman in the World" for FHM's100 Sexiest Women poll.[180] In 1997, she was chosen by People magazine as one of the 50 Most Beautiful People in the World.[181]Askmen listed her at No. 6 on their Top 7: '90s Sex Symbols.[182] In 2008, she was listed 21st in FHM's All Time 100 Sexiest Hall of Fame.[183] In 2016, Anderson was named one of World's Most Beautiful Faces of the Year by People magazine.[184]